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I asked this question a long while ago, but I never got an answer to whether mental exhaustion can be measured. If mental exhaustion could be measured, it would mean that I would have a way of knowing the performance I can get out of my brain in a day. I would be able to know what is best for refilling my brain with energy (maybe TV is your best option after all...;) ) As far as I understand, different parts of the brain gets used for different purposes, so they should get exhausted at different times, so the measuring would have to be on specific regions of the brain or performance of the brain in various fields.

"If mental exhaustion could be measured, it would mean that I would have a way of knowing the performance I can get out of my brain in a day.". That's jumping to conclusions a bit too quickly. "As far as I understand, different parts of the brain gets used for different purposes, so they should get exhausted at different times", could you provide a reference for this?
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Steven Jeuris♦Jan 21 '12 at 20:26

@StevenJeuris 1. If one can measure something accurately, one could take the average performance per day, and that would be my prediction. 2. I thought this was common knowledge, but I am happy to remove it if you do not believe it is.
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DavidJan 21 '12 at 21:26

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@David: It might just be a wording issue. I don't know enough about the subject in order to judge about the validity, but I do know your question gives the impression of making a lot of assumptions. A good question should clearly indicate on what it is based. We are still composing guidelines for this, so feel free to give your own input on meta. I was particularly worried about the fact the actual question is 'Can it be measured?', followed by what to me seem to be assumptions. ("they should get exhausted at different times")
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Steven Jeuris♦Jan 21 '12 at 21:48

2 Answers
2

A serial addition/subtraction task was included in the assessment
battery to measure cognitive throughput. The serial
addition/subtraction task is a subject-paced task requiring the
completion of 50 mental arithmetic trials. The average number of
correct responses per min was used as a neurobehavioral assay of
cognitive throughput performance.

Second, alertness / vigilance (response time to stimuli):

The neurobehavioral assessment battery included a psychomotor
vigilance task to measure behavioral alertness. The psychomotor
vigilance task (PVT) is a sustained-attention reaction time task with
a random inter-stimulus interval of 2–10 s. Lapses (reaction times
greater than 500 ms) were counted per 10 min test bout as a measure of
performance.

Third, memory:

The neurobehavioral assessment battery also included a computerized
digit symbol substitution task to measure working memory. This
subject-paced task involves the matching of digits (0–9) to symbols
(circle, triangle, etc.). The number of correct responses in 1.5 min
was counted to measure working memory performance.

The metrics ought to be effective for measuring mental performance due to fatigue whatever the cause of fatigue might be.

There are a several perspectives of mental fatigue. Here are a few starting points:

There is a huge literature on burnout (see wikipedia article for a review, and Maslach et al, 2001, PDF) for their annual review of psychology article. Burnout refers to a rather chronic form of emotional and mental exhaustion. Burnout is often assessed in research using questionnaires, but obviously it could be clinically assessed. Of course, your question seems more concerned with short term fatigue rather than longer term fatigue, and cognitive fatigue rather than emotional fatigue.

There are a lot of studies looking at fatigue and work hours (see this google scholar search). Such studies are often conducted within the context of human factors, occupational health, and work stress perspectives. You might like this one by Folkard et al (2003, PDF) on shift work, safety and productivity, it has some graphs relating time of day and time since break to productivity (i.e., not exactly answering your question, but marginally relevant).

You could look at the literature on vigilance that discusses the general deterioration of vigilance skills over time (see this wikipedia discussion).